Process and catalyst for propylene ammoxidation to acrylonitrile

ABSTRACT

Olefins such as propylene and isobutylene are converted to the corresponding unsaturated nitriles, acrylonitrile, and methacrylonitrile, respectively, by reacting a mixture of the olefin, ammonia, and molecular oxygen-containing gas in the presence of a catalyst containing the oxides of molybdenum, bismuth, iron, cobalt, nickel, and chromium, and either phosphorus or antimony or mixtures thereof, and an alkali metal or mixture thereof, and optionally one element selected from the group of an alkaline earth metal, a rare earth metal, niobium, thallium, arsenic, magnesium, zinc, cadmium, vanadium, boron, calcium, tin, germanium, manganese, tungsten, tellurium, or mixtures thereof.

This is a division of co-pending application Ser. No. 07/495,875 filed Mar. 19, 1990, now U.S. Pat. No. 5,134,105.

This invention relates to an improved process and catalyst for the ammoxidation of olefin-ammonia mixtures to unsaturated nitriles, and more particularly to an improved process and catalyst for the ammoxidation of propylene-ammonia and isobutylene-ammonia to acrylonitrile and methacrylonitrile, respectively. The ammoxidation is conducted in the presence of a catalyst comprising the oxides of molybdenum, bismuth, iron, cobalt, nickel, and chromium, and either phosphorus or antimony or mixtures thereof and an alkali metal or mixture thereof, and optionally one element selected from the group of an alkaline earth metal, a rare earth metal, niobium, thallium, arsenic, magnesium, zinc, cadmium, vanadium, boron, calcium, tin, germanium, manganese, tungsten, tellurium, or mixtures thereof. It is also envisioned that the catalyst of this invention would effectively function as a catalyst for fluid bed oxidation of propylene to acrolein. For example, the catalyst would function in the processes of U.S. Pat. Nos. 4,230,640 and 4,267,385 herein incorporated by reference.

There are many patents related to the production of acrylonitrile using a bismuth-molybdenum-iron fluidized bed catalyst (e.g., U.S. Pat. No. 3,642,930). In particular, U.S. Pat. No. 3,911,089 issued Oct. 7, 1975 discloses a process for acrylonitrile production using a catalyst comprised of the oxides of molybdenum, and bismuth, and optionally iron, and optionally the oxides of chromium, manganese, cobalt, nickel, zinc, cadmium, tin, tungsten, lead or mixtures thereof, and optionally thallium, a group IA or IIA element and optionally phosphorus, arsenic, antimony or mixtures thereof.

The catalyst employed in the process of this invention has high activity for the production of unsaturated nitriles at a slightly lower reaction temperature than is normally employed for this type of process, and continues efficient low temperature operation after aging. In addition to high activity for nitrile production, the catalyst has a number of other important advantages that contribute greatly to the efficient and economic operation of the process. The catalyst has excellent redox stability under the reaction conditions of the process. This permits the use of low process air to olefin ratios and high weight hourly space velocities. The catalyst exhibits efficient ammonia utilization thus greatly reducing the amount of unreacted ammonia appearing in the reactor effluent and thus lowering the amount of sulfuric acid required to neutralize the ammonia in the effluent. This results in improvements in (1) the operation of the recovery section of the process and (2) pollution control. The use of lower operating temperatures favors longer catalyst life and minimizes effluent problems such as afterburning. Despite the lower reaction temperatures, per pass conversions to the nitrile product of 80 percent and above are obtained. A further important advantage associated with the catalyst of this invention is the low cost of the essential catalytic components and the ease of catalyst preparation.

The reactants employed in producing the unsaturated nitriles of this invention are oxygen, ammonia, and an olefin having three carbon atoms in a straight chain such as propylene or isobutylene, and mixtures thereof.

The olefins may be in a mixture with paraffinic hydrocarbons, such as ethane, propane, butane and pentane; for example, a propylenepropane mixture may constitute the feed. This makes it possible to use ordinary refinery streams without special separation, although the effectiveness of conversion would be diminished. Likewise, diluents such as nitrogen and oxides of carbon may be present in the reaction mixture without deleterious effect.

In its preferred aspect, the process comprises contacting a mixture comprising propylene or isobutylene, ammonia and oxygen with the catalyst at an elevated temperature and at atmospheric or near atmospheric pressure to produce acrylonitrile or methacrylonitrile. Most preferably, the process is directed to contacting propylene, ammonia and oxygen with a fluid bed catalyst at an elevated temperature to produce acrylonitrile.

Any source of oxygen may be employed in this process. For economic reasons, however, it is preferred that air be employed as the source of oxygen. From a purely technical viewpoint, relatively pure molecular oxygen will give equivalent results. The molar ratio of oxygen to the olefin in the feed to the reaction vessel should be in the range of 0.2:1 to 3.0 and a ratio of about 1.5 to 2.5 is preferred.

The molar ratio of ammonia to olefin in the feed to the reaction vessel may vary between about 0.5:1 to 5:1, preferably 0.9:1 to 1.3:1. There is no real upper limit for the ammonia-olefin ratio, but there is generally no reason to exceed a ratio of 1.3:1. At ammonia-olefin ratios appreciably less than the stoichiometric ratio of 1:1, various amounts of oxygenated derivatives of the olefin will be formed. Outside the upper limit of this range only insignificant amounts of aldehydes and acids will be produced, and reduced amounts of nitriles will be produced at ammonia-olefin ratios below the lower limit of this range. It is surprising that within the ammonia-olefin range stated, maximum utilization of ammonia is obtained, and this is highly desirable. It is generally possible to recycle any unreacted olefin and unconverted ammonia.

In some cases water in the mixture fed to the reaction vessel improves the selectivity of the reaction and yield of nitrile. However, addition of water to the feed is not essential in this invention, inasmuch as water is formed in the course of the reaction.

In general, the molar ratio of added water to olefin, when water is added, is above about 0.25:1. Ratios on the order of 1:1 to 4:1 are particularly desirable, but higher ratios may be employed, i.e., up to about 10:1.

The reaction is carried out at a temperature within the range of from about 300° to about 600° C. The preferred temperature range is from about 380° to 500° C., especially preferred being from about 400° to 480° C.

The pressure at which the reaction is conducted is another variable. The reaction may be carried out at any pressure, however, preferably it is carried out at about atmospheric or above atmospheric pressure (2 to 5 atmospheres).

The apparent contact time is not critical, and contact times in the range of from 0.1 to about 50 seconds may be employed. The optimum contact time will, of course, vary depending upon the olefin being reacted, but in general, a contact time of from 1 to 15 seconds is preferred.

Generally any apparatus of the type suitable for carrying out oxidation/ammoxidation reactions in the vapor phase may be employed in the execution of this process. The process may be conducted either continuously or intermittently. The catalyst bed may be a fixed-bed employing a large particulate or pelleted catalyst or preferably, a so-called "fluidized" bed of catalyst may be employed. Any conventional fluid ammoxidation reactor may be utilized in the practice of the process of the present invention. For example, the reactor described in U.S. Pat. No. 3,230,246, issued Jan. 18, 1966 incorporated herein by reference would be suitable in the practice of the present invention. Furthermore, conventional transfer line reactors may be used.

The reactor may be brought to the reaction temperature before or after the introduction of the reaction feed mixture. However, in a large scale operation it is preferred to carry out the process in a continuous manner, and in such a system the recirculation of the unreacted olefin is contemplated. Periodic regeneration or reactivation of the catalyst is also contemplated, and this may be accomplished, for example, by contacting the catalyst with air at an elevated temperature.

The products of the reaction may be recovered by any of the methods known to those skilled in the art. One such method involves scrubbing the effluent gases from the reactor with cold water or an appropriate solvent to remove the products of the reaction. If desired, acidified water can be used to absorb the products of the reaction and neutralize unconverted ammonia. The ultimate recovery of the products may be accomplished by conventional means. The efficiency of the scrubbing operation may be improved when water is employed as the scrubbing agent by adding a suitable wetting agent in the water. Where molecular oxygen is employed as the oxidizing agent in this process, the resulting product mixture after the removal of the nitriles may be treated to remove carbon dioxide, with the remainder of the mixture containing the unreacted olefin and oxygen being recycled through the reactor. In the case where air is employed as the oxidizing agent in lieu of molecular oxygen, the residual product after separation of the nitriles and other carbonyl products may be scrubbed with a non-polar solvent, e.g., a hydrocarbon fraction in order to recover unreacted olefin, and in this case the remaining gases may be discarded. The addition of a suitable inhibitor to prevent polymerization of the unsaturated products during the recovery steps is also contemplated.

The catalyst useful in the process of the present invention is a mixture, compound or possibly complex of the oxides of molybdenum, bismuth, iron, cobalt, nickel, chromium, and either phosphorus or antimony or mixtures thereof, and an alkali metal or mixture thereof, and optionally an alkaline earth, a rare earth metal, niobium, thallium, arsenic, magnesium, zinc, cadmium, vanadium, boron, calcium, tin, germanium, manganese, tungsten, tellurium or mixtures thereof. The composition is characterized by the following empirical formula:

    Mo.sub.a Bi.sub.b Fe.sub.c Co.sub.d Ni.sub.e Cr.sub.f X.sub.g Y.sub.i Z.sub.j O.sub.k

wherein X is one or more of the elements selected from the group comprising phosphorus or antimony or mixture thereof, and Y is an alkali metal or mixture thereof, and Z is an alkaline earth metal, a rare earth metal, niobium, thallium, arsenic, magnesium, zinc, cadmium, vanadium, boron, calcium, tin, germanium, manganese, tungsten, tellurium or mixtures thereof, wherein (a) is a number from 12-14, (b) is a number from 1-5, (c) is a number from 0.5-5, (d) and (e) are numbers from 0.1-6, (f) is a number from 0.1-4, (g) is a number from 0.1-4, (i) is a number from 0.1-2, (j) is a number from 0-3, and (k) is a number determined by the valence requirements of the other elements present. Preferably (g) is a number from 0.75 to 3. Preferably, when Y is an alkali metal other than sodium, (i) is a number from 0.1-1.5. Furthermore, the catalyst generally has a surface area of less than 100 M² /g, preferably about 20 M² /g to about 50 M² /g.

The catalyst of this invention may be prepared by any of the numerous methods of catalyst preparation which are known to those skilled in the art. For example, the catalyst may be manufactured by co-precipitating the various ingredients. The co-precipitated mass may then be dried and ground to an appropriate size. Alternately, the co-precipitated material may be slurried and spray-dried in accordance with conventional techniques. The catalyst may be extruded as pellets or formed into spheres in oil as is well-known in the art. Alternatively, the catalyst components may be mixed with the support in the form of the slurry followed by drying, or they may be impregnated on silica or other supports.

A particularly attrition-resistant form of the catalyst may be prepared by adding the support material to the catalyst in two stages, first by preparing and heat-treating a mixture of active catalyst components and from 0 to 60% by weight of the total support material, followed by adding the remainder of the support material to the powdered form of the heat-treated catalyst.

The alkali metal may be introduced into the catalyst as an oxide or as any salt which upon calcination will yield the oxide. Preferred salts are the nitrates which are readily available and easily soluble.

Bismuth may be introduced into the catalyst as an oxide or as any salt which upon calcination will yield the oxide. Preferred are the water-soluble salts which are easily dispersible within the catalyst and which form stable oxides upon heat treating. A source for introducing bismuth is bismuth nitrate which has been dissolved in a dilute solution of HNO₃. It is also especially preferred to dissolve bismuth nitrate in a metal nitrate melt.

To introduce the iron component into the catalyst one may use any compound of iron which, upon calcination, will result in the oxides. As with the other elements, water-soluble salts are preferred for the ease with which they may be uniformly dispersed within the catalyst. Most preferred is ferric nitrate. Cobalt and nickel may be similarly introduced.

To introduce the molybdenum component, any molybdenum oxide such as the dioxide, trioxide, pentoxide, or sesquioxide may be used; more preferred is a hydrolyzable or decomposable molybdenum salt. The most preferred starting material is ammonium heptamolybdate (AHM).

Phosphorus may be introduced as an alkali metal salt, an alkaline earth metal salt or the ammonium salt, but is preferably introduced as phosphoric acid. The most preferred method is the use of phosphomolybdic acid which also introduces molybdenum.

Other elements may be introduced, starting with the metal, oxidizing the metal with an oxidizing acid such as nitric acid, and then incorporating the nitrate into the catalyst. Generally, however, the nitrates are readily available and form a very convenient starting material.

Other variations in starting materials will suggest themselves to one skilled in the art, particularly when the preferred starting materials mentioned herein above are unsuited to the economics of large-scale manufacture. In general, any compounds containing the desired catalyst components may be used provided that they result in the oxides of the instant catalyst upon heating to a temperature within the range disclosed hereinafter.

The catalyst can be employed without a support and will display excellent activity. The catalyst can also be combined with a support, and preferably it is combined with at least 10 percent up to about 90 percent of the supporting compound by weight of the entire composition. Any known support materials can be used, such as, silica, alumina, zirconia, titania, ALUNDUM, silicon carbide, alumina-silica, the inorganic phosphates such as aluminum phosphate, silicates, aluminates, borates, carbonates, and materials such as pumice, montmorillonite, and the like that are stable under the reaction conditions to be encountered in the use of the catalyst. Aerosil may also be added to the support material. The preferred support is silica, which is added to the slurry during the preparation of the catalyst in the form of silica sol or fumed silica. The level of support is usually in the range of 10-70% weight present. Preferably, the level of support is in the range of 40-60% weight present.

The catalytic activity of the system is enhanced by heating at an elevated temperature. Generally, the catalyst mixture is spray dried at a temperature of between about 110° C. to 350° C. and then heat treated in stages for from about one to twenty-four hours or more at a temperature of from about 260° to about 1000° C., preferably from 300°-400° C. to 550°-700° C.

In general, calcination of the catalyst is achieved in less time at higher temperatures. The sufficiency of calcination at any given set of conditions is ascertained by a spot test of a sample of the material for catalytic activity. Calcination is best carried out in an open chamber, permitting circulation of air or oxygen, so that any oxygen consumed can be replaced.

Further, pre-treatment or activation of the catalyst before use with a reducing agent such as ammonia in the presence of a limited amount of air at a temperature in the range of 260° to 540° C. is also used.

A preferred method of preparing the catalyst of this invention and a more complete description of the process of the invention can be obtained from the following examples. In addition to the production of unsaturated nitriles, the catalyst of this invention is also useful for the conversion of olefins, such as propylene and isobutylene, to the corresponding unsaturated aldehydes and unsaturated carboxylic acids.

EXAMPLES 1 TO 8

The catalysts employed in the examples of this invention were prepared by the procedure described below.

EXAMPLE 1

Metal nitrates in the following order were melted together at .sup.˜ 70° C. in a 400 ml beaker Fe(NO₃)₃.9H₂ O (65.08 g), Co(NO₃)₂.6H₂ O (121.89 g), Ni(NO₃)₂.6H₂ O (65.57 g)(AHM), Bi(NO₃).₃ 5H₂ O (65.24 g), KNO₃ (1.63 g). The (NH₄)₆ MoO₂₄.4H₂ O (184.85 g) was dissolved in 300 ml of distilled water followed by the addition of the CrO₃ (8.05 g). To this solution the metal nitrates melt was added, followed by the 40% silica sol (625 g). The resultant yellow slurry was heated by stirring at .sup.˜ 90° C. for .sup.˜ 3 hours, then the slurry was spray dried. The obtained material was denitrified at 270° C. for 2 hours and at 425° C. for 2 hours and then was calcined at 580° C. for 2 hours in air.

EXAMPLE 2

Metal nitrates were melted at .sup.˜ 70° C. in a 400 ml breaker in the following order Fe(NO₃)₃.9H₂ O (65.10 g), Co(NO₃)₂.6H₂ O (121.93 g), Ni(NO₃)₂.6H₂ O (65.6 g), Bi(NO₃).₃ 5H₂ O (65.20 g), KNO₃ (1.63 g). The AHM (184.91 g) was dissolved in 300 ml of distilled water followed by the addition of the CrO₃ (6.24 g) and 85% H₃ PO₄ (1.86 g). To this solution the metal nitrates melt was added followed by the 40% silica sol (625 g). The resultant yellow slurry was heated by stirring at .sup.˜ 90° C. for .sup.˜ 3 hours, then the slurry was spray dried. The obtained material was denitrified at 270° C. for 2 hours and 425° C. for 2 hours and then was calcined in air at 580° C. for 2 hours.

EXAMPLE 3

Metal nitrates in the following order were melted together at .sup.˜ 70° C. in a 400 ml beaker Fe(NO₃)₃.9H₂ O(65.1 g), Co(NO₃)₂.6H₂ O(121.9 g), Ni(NO₃)₂.6H₂ O (65.6 g), Bi(NO₃)₃ 5H₂ O (65.3 g), KNO₃ (1.6 g). The AHM (184.9 g) was dissolved in 300 ml of distilled water followed by the addition of the CrO₃ (4.0 g) and 85% H₃ PO₄ (4.65 g). To this solution the metal nitrate melt was added, followed by the 40% silica sol (625 g). The resultant yellow slurry was heated by stirring at .sup.˜ 90° C. for .sup.˜ 3 hours, then the slurry was spray dried. The obtained material was denitrified at 270° C. for 2 hours and 425° C. for 2 hours and then was calcined in air at 580° C. for 2 hours.

EXAMPLE 4

Metal nitrates were melted together at .sup.˜ 70° C. in a 400 ml beaker in the following order Fe(NO₃)₃.9H₂ O (65.15 g), Co(NO₃)₂.6H₂ O (122.0 g), Ni(NO₃)₂.6H₂ O (63.3 g), Bi(NO₃)₃.5H₂ O (65.3 g), KNO₃ (.8 g), Cs(NO₃) (1.26 g). The AHM (185.06 g) was dissolved in 300 ml of distilled water followed by the addition of CrO₃ (4.03 g) and 85% H₃ PO₄ (4.65 g). The metal nitrates melt was added to this solution followed by the 40% silica sol (625 g). The resultant yellow slurry was heated at .sup.˜ 90° C. for .sup.˜3 hours, then the slurry was spray dried. The obtained material was denitrified at 270° C. for 2 hours and 425° C. for 2 hours and then was calcined at 580° C. for 2 hours in air.

EXAMPLE 5

Metal nitrates were melted together at .sup.˜ 70° C. in a 400 ml beaker in the following order Fe(NO₃)₃.9H₂ O (62.21 g), Co(NO₃)₂.6H₂ O (116.51 g), Ni(NO₃)₂.6H₂ O (62.68 g), Bi(NO₃)₃.5H₂ O (62.36 g), KNO₃ (1.56 g). The AHM (176.7 g) was dissolved in 300 ml of distilled water followed by the addition of CrO₃ (3.85 g) and 85% H₃ PO₄ (4.44 g). To this solution the metal nitrates melt was added followed by the Sb₂ O₃ (11.22 g) and the 40% silica sol (625 g). The resultant yellow slurry was heated at .sup.˜ 90° C. for .sup.˜ 3 hours, then the slurry was spray dried. The obtained material was denitrified at 270° C. for 2 hour and 425° C. for 2 hours and then was calcined at 580° C. for 2 hours in air.

EXAMPLE 6

Metal nitrates were melted together at .sup.˜ 70° C. in a 400 ml beaker in the following order Fe(NO₃)₃.9H₂ O (59.3 g), Co(NO₃)₂.6H₂ O (111.0 g), Ni(NO₃)₂.6H₂ O (59.7 g), Bi(NO₃)₃.5H₂ O (59.4 g), KNO₃ (1.5 g). The AHM (168.4 g) was dissolved in 300 ml of distilled water followed by the addition of CrO₃ (3.7 g) and 85% H₃ PO₄ (4.2 g). To this solution the metal nitrates melt was added followed by the Sb₂ O₃ (22.5 g) and the 40% silica sol (625 g). The resultant yellow slurry was heated at .sup.˜ 90° C. for .sup.˜ 3 hours, then the slurry was spray dried. The obtained material was denitrified at 270° C. for 2 hours and 425° C. for 2 hours and then was calcined at 580° C. for 2 hours in air.

EXAMPLE 7

Metal nitrates were melted together at .sup.˜ 70° C. in a 400 ml beaker in the following order Fe(NO₃)₃.9H₂ O (62.22 g), Co(NO₃)₂.6H₂ O (116.54 g), Ni(NO₃)₂.6H₂ O (60.46 g), Bi(NO₃)₃.5H₂ O (62.38 g), KNO₃ (.78 g) and Cs(NO₃) (1.20 g). The AHM (176.75 g) was dissolved in 300 ml of distilled water followed by the addition of CrO₃ (3.85 g) and 85% H₃ PO₄ (4.44 g). To this solution the metal nitrates melt was added followed by Sb₂ O₃ (11.22 g) and 40% silica sol (625 g). The resultant yellow slurry was heated at .sup.˜ 90° C. for 3 hours, then the slurry was spray dried. The obtained material was denitrified at 270° C. for 2 hours and 425° C. for 2 hours and then was calcined at 580° C. for 2 hours in air.

EXAMPLE 8

Metal nitrates were melted together at .sup.˜ 70° C. in a 400 ml beaker in the following order Fe(NO₃)₃.9H₂ O(59.3 g), Co(NO₃)₂.6H₂ O(111.0 g), Ni(NO₃)₂.6H₂ O (57.6 g), Bi(NO₃)₃.5H₂ O (59.4 g), KNO₃ (0.7 g), and Cs(NO₃)(1.2 g). The AHM (168.3 g) was dissolved in 300 ml of distilled water followed by the addition of CrO₃ (3.7 g) and 85% H₃ PO₄ (4.2 g). To this solution the metal nitrates melt was added followed by Sb₂ O₃ (22.4 g) and 40% silica sol (625 g). The resultant yellow slurry was heated at .sup.˜ 90° C. for 3 hours, then the slurry was spray dried. The obtained material was denitrified at 270° C. for 2 hours and 425° C. for 2 hours and then was calcined at 580° C. for 2 hours in air.

In the examples given, percent conversion to the unsaturated nitrile is defined as follows:

Mole percent per pass conversion (PPC) to unsaturated nitrile= ##EQU1##

Ammoxidation reactions carried out with catalyst compositions prepared by the method of Examples 1-8 and employing propylene as the hydrocarbon feeds are summarized in Table I. Each reaction was run in a 40 cc fluid bed reactor. Each catalyst was initially reduced by NH₃ /N₂ at 440° C. for ten minutes. After a stabilization period of approximately 40 hours, samples were collected.

Reactor effluent was collected in bubble-type scrubbers containing a cold HCl solution. Off-gas rate was measured with a soap filmmeter, and the off-gas composition was determined at the end of the run with the aid of a Perkin-Elmer Model 154 gas chromatograph fitted with a split column gas analyzer.

At the end of the recovery run, the entire scrubber liquid was diluted to approximately 200 grams with distilled water. A weighted amount of MEK was used as an internal standard in a .sup.˜ 50 gram aliquot of the dilute solution.

A 6 micro liter sample was analyzed in a 5710 Hewlett-Packard gas chromatograph fitted with a flame ionization detector and a carbopak column. The amount of HCN was determined by titration with AgNO₃.

                                      TABLE I                                      __________________________________________________________________________     Ex-                              Temp.                                                                              AN   HCN  CO.sub.2                                                                            CO   Selectivity           ample                                                                              Catalyst Composition         (°C.)                                                                       (% ppc)                                                                             (% ppc)                                                                             (% ppc)                                                                             (% ppc)                                                                             to AN                 __________________________________________________________________________                                                              (%)                   1   50%Mo.sub.13 Bi.sub.1.67 Fe.sub.2.0 Co.sub.5.2 Ni.sub.2.8 K.sub..2             Cr.sub.1.0 O.sub.x *50%SiO.sub.2                                                                            435 76.2 6.6  6.7  2.9  78.2                  2   50%Mo.sub.13 Bi.sub.1.67 Fe.sub.2.0 Co.sub.5.2 Ni.sub.2.8 K.sub..2             Cr.sub..8 P.sub..2 O.sub.x *50%SiO.sub.2                                                                    435 77.7 6.8  6.5  2.8  78.9                  3   50%Mo.sub.13 Bi.sub.1.67 Fe.sub.2.0 Co.sub.5.2 Ni.sub.2.8 K.sub..2             Cr.sub..5 P.sub..5 O.sub.x *50%SiO.sub.2                                                                    435 78.0 6.3  6.3  3.1  80.3                  4   50%Mo.sub.13 Bi.sub.1.67 Fe.sub.2.0 Co.sub.5.2 Ni.sub.2.8 K.sub..1             Cs.sub..08 Cr.sub..5 P.sub..5 O.sub.x *50%SiO.sub.2                                                         435 79.1 5.8  5.4  2.6  81.6                  5   50%Mo.sub.13 Bi.sub.1.67 Fe.sub.2.0 Co.sub.5.2 Ni.sub.2.8 K.sub..2             Cr.sub..5 P.sub..5 Sb.sub.1.0 O.sub.x *50%SiO.sub.2                                                         435 78.3 5.4  5.4  2.7  81.2                  6   50%Mo.sub.13 Bi.sub.1.67 Fe.sub.2.0 Co.sub.5.2 Ni.sub.2.8 K.sub..2             Cr.sub..5 P.sub..5 Sb.sub.2.1 O.sub.x *50%SiO.sub.2                                                         430 80.2 5.5  6.0  2.9  81.8                  7   50%Mo.sub.13 Bi.sub.1.67 Fe.sub.2.0 Co.sub.5.2 Ni.sub.2.8 K.sub..1             Cs.sub..08 P.sub..5 Sb.sub.1.0 O.sub.x *50%SiO.sub.2                                                        435 79.4 3.9  5.7  2.7  82.6                  8   50%Mo.sub.13 Bi.sub.1.67 Fe.sub.2.0 Co.sub.5.2 Ni.sub.2.8 K.sub..1             Cs.sub..08 P.sub..5 Sb.sub.2.1 O.sub.x *50%SiO.sub.2                                                        435 80.2 5.0  5.3  2.4  83.2                  __________________________________________________________________________ 

What is claimed:
 1. In the process for the conversion of an olefin selected from the group consisting of propylene, isobutylene and mixtures thereof, to acrylonitrile, methacrylonitrile and mixtures thereof respectively by reacting in the vapor phase at a temperature of from about 300° C. to 600° C. and at an elevated pressure, said olefin with a molecular oxygen-containing gas and ammonia in the presence of a oxide catalyst, the improvement comprising:conducting the reaction in the presence of a catalyst having the following empirical formula:

    Mo.sub.a Bi.sub.b Fe.sub.c Co.sub.d Ni.sub.e Cr.sub.f X.sub.g Y.sub.i Z.sub.j O.sub.k

wherein X is a mixture of P and Sb; Y is an alkali metal or mixture thereof; Z is an alkaline earth metal, a rare earth metal, Nb, Tl, As, Zn, Cd, V, B, Sn, Ge, Mn, W, Te or mixture thereof; andwherein a is a number from 12 to 14; b is a number from 1 to 5; c is a number from 0.5 to 5; d and e are numbers from 0.1 to 6; f is a number from 0.1 to 4; g is a number from 0.1 to 4; i is a number from 0.1 to 2; j is a number from 0 to 3; and k is a number determined by the valence requirements of the other elements present.
 2. The process of claim 1 wherein said temperature is from about 400° C. to about 480° C.
 3. The process of claim 1 wherein g is a number from 0.75 to
 3. 4. The process of claim 1 wherein said catalyst is supported on a catalyst support material selected from the group consisting of silica, alumina, zirconia, titania, ALUNDUM, silicon carbide, aluminasilica, inorganic phosphates, pumice, montmorillonite or mixtures thereof.
 5. The process of claim 2 wherein said support material is silica.
 6. The process of claim 2 wherein said support is 10-70% by weight of said catalyst.
 7. The process of claim 5 wherein said support is 40-60% by weight of said catalyst.
 8. The process of claim 1 wherein said molecular oxygen-containing gas is air.
 9. The process of claim 1 wherein said olefin is propylene.
 10. The process of claim 9 wherein said olefin is isobutylene.
 11. The process of claim 1 wherein the molar ratios of oxygen:olefin are within the range of about 0.2:1 to 3.0:1.
 12. The process of claim 1 wherein the molar ratios of ammonia:olefin are within the range of about 0.9:1 to 1.3:1.
 13. The process of claim 11 wherein the molar ratios of oxygen:olefin are within the range of about 1.5:1 to 2.5:1.
 14. The process of claim 12 carried out in the presence of steam.
 15. The process of claim 1 carried out in a fluid bed reactor. 